A communication protocol called WebSocket is known as a web-standard communication protocol that enables maintaining any established connection and achieving reduction in the delay during a connection establishment operation, and therefore enables performing low-delay communication. A WebSocket server has a limitation on the number of connections that can be independently retained. Hence, it is common practice to configure a system with a plurality of servers. In that regard, a technology is known in which two terminal devices capable of performing two-way communication establish a connection with the same WebSocket server so that the two-way communication concludes in a single server and the delay is held down to only a small amount.
In order for a WebSocket server to stay connected with the terminal devices, connection information and a transmission-reception buffer needs to be secured in the WebSocket server. For that reason, an increase in the number of connections to be maintained by a WebSocket server leads to an increase in the server operation cost. On the other hand, there is a method available in which the terminal devices periodically access a server (periodically perform polling) to maintain a communicable state. However, in this method, it is more likely to have a delay in communication as compared to the connection maintenance method implemented in a WebSocket server. Therefore, there is a demand to achieve low-delay communication while holding down the number of connections to be maintained by a WebSocket server.